\documentclass{report}

\usepackage[numbers]{natbib}
\usepackage{comment}
\usepackage{url}

\newcommand{\sharedReport}{}

\input{\sharedReport preamble}

\begin{document}
\sharedInput{introSecs}
\sharedInput{related_work}
\sharedInput{initial_analysis}
\sharedInput{system_statement}
\sharedInput{methods}
\bibliographystyle{plainnat}
\bibliography{bib}
\end{document}